(1) Field of the Invention
This invention relates to an adhesive composition, and a composite such as, for example, a belt which is comprised of a fibrous material, treated with the adhesive composition, and a nitrile group-containing highly saturated copolymer rubber.
(2) Description of the Related Art
Belts such as an automobile timing belt, a poly-ribbed belt, a lapped belt and a V-belt are made of a composite comprised of a base fibrous material usually in a fabric form and a rubber. As the rubber, chloroprene rubber (CR) and an acrylonitrile-butadiene copolymer rubber (NBR), which have a good oil resistance, heretofore have been widely used. But, recently, there is an increasing demand for a nitrile group-containing highly saturated copolymer rubber which has good heat resistance as well as good oil resistance and thus meets requirements such as regulations for automobile exhaust gas, minimization of an engine room for weight-saving of an automobile, and encasement of an engine room for noise reduction.
Taking a timing belt as an example of the belts, the geared portion thereof is reinforced with a nylon canvas. The nylon canvas is treated with a rubber cement in an organic solvent for minimizing the abrasion of the belt caused by toothing with gears, and for enhancing the adhesion between the canvas and the rubber. However, in recent years, the treatment of an organic solvent has caused a problem of environmental pollution, and thus, a treatment with an aqueous rubber cement is now desired.
As adhesives for a nitrile group-containing highly saturated copolymer rubber with a fibrous material, there have heretofore been proposed an adhesive composition comprising a latex of a nitrile group-containing highly saturated copolymer rubber having an iodine value of not larger than 120 and a resorcinol-formaldehyde resin (Japanese Unexamined Patent Publication No. 63-248879); and an adhesive composition comprising a nitrile group-containing highly saturated copolymer rubber latex and a resorcinol-formaldehyde resin, which rubber latex is made by selectively hydrogenating the carbon-to-carbon double bonds of a nitrile group-containing unsaturated copolymer rubber in a latex, obtained by an emulsion polymerization procedure, in the presence of a hydrogenation catalyst (Japanese Unexamined Patent Publication No. 3-167239). The proposed adhesive compositions are aqueous and thus the problem of environmental pollution does not arise. Further, the fibrous material having been treated with these adhesive compositions exhibits an enhanced adhesion to the nitrile group-containing highly saturated copolymer rubber.
However, the fibrous material, which has been treated with the above-mentioned adhesive composition comprising the nitrile group-containing highly saturated copolymer rubber latex and a resorcinol-formaldehyde resin, has a poor abrasion resistance as compared with the fibrous material treated with an organic solvent-containing rubber cement. Especially where the above-mentioned adhesive composition comprising the nitrile group-containing highly saturated copolymer rubber latex and a resorcinol-formaldehyde resin is used for treating a canvas for a belt, the resulting belt has a poor abrasion resistance.